Boiling heat transfer device

ABSTRACT

A boiling heat transfer device of the present invention includes: a heat receiving portion that boils a liquefied refrigerant to convert it to vapor, and contacts with a device to be cooled and cools the device to be cooled; a vapor tube that connects to an upper portion of the heat receiving portion and conveys the vapor generated by the heat receiving portion; a heat dissipating portion that condenses the vapor conveyed from the vapor tube to convert it to a liquefied refrigerant and dissipates heat to an atmosphere; and a liquid tube that returns to the heat receiving portion the liquefied refrigerant condensed by the heat dissipating portion. At least a portion of a cross-sectional area of a flow passage of the vapor in the heat receiving portion gradually decreases from a lower portion of the heat receiving portion toward the upper portion of the heat receiving portion.

The present application is a continuation application of U.S. patentapplication Ser. No. 13/128,740 filed on May 11, 2011, which is aNational Stage Entry of international application PCT/JP2009/00557,filed on Oct. 22, 2009, which claims priority from Japanese PatentApplication No. 2008-294282 filed on Nov. 18, 2008, the disclosure ofall of which are incorporated in their entirely by reference herein.

TECHNICAL FIELD

The present invention relates to a boiling heat transfer device forcooling a semiconductor device and electronic devices, and in particularto a boiling heat transfer device that circulates a refrigerant byutilizing the gas-liquid phase transition phenomenon.

BACKGROUND ART

In order to dissipate a large quantity of heat that is generated in asemiconductor device or electronic devices, a method has been developedto obtain a high cooling performance by bringing a heat absorber intocontact with such heat generating devices, and flowing a refrigerantinside of the heat absorber. By boiling the refrigerant with the heatabsorber, it is possible to obtain a higher cooling effect. As a methodof circulating the refrigerant between the heat absorbing portion andthe heat dissipating portion, traditionally a method that employs a pumpwas generally used. In the case of a boiling heat transfer device, athermal siphon-type cooling structure has been proposed that, byinstalling a heat absorbing portion in the lower part of the cooler anda heat dissipating portion above the cooler, does not required a pump byemploying the principle of vapor collecting upward with respect to thedirection of gravity due to the difference in density between the vaporthat is generated and the liquid (for example, refer to Patent Documents1 to 5).

The boiling heat transfer device that is disclosed in Patent Document 1has a thin-type refrigerant bath whose planar shape is almosttrapezoidal, with a boiling space provided within. The portion thatcomes into contact with a heat generator (computer chip) is provided onthe bottom surface of the refrigerant bath, and a vapor side header tankand a liquid side header tank that extend from the refrigerant tank in aperpendicular direction and are continuous with the interior space ofthe refrigerant tank are provided on the upper surface of therefrigerant tank. Both header tanks are connected by a plurality of heatdissipating tubes. Heat dissipating fins are installed between the heatdissipating tubes. In this boiling heat transfer device, the portion ofthe refrigerant tank that is in contact with the heat generator isprovided along the upper base of the trapezoid shape, and the connectionportion between the gas side/liquid side header tanks of the refrigeranttank is provided near the end portions on the lower base of thetrapezoid shape.

Patent Document 2 discloses a CPU cooling device that leads refrigerantvapor from a vaporizer that is in contact with a CPU, which is a heatgenerator, to a condenser via a vapor flow passage, and returns therefrigerant that has been liquefied in the condenser to the vaporizervia a liquid flow passage. In the cooling device, a zigzagging pipe thatis provided in a manner connected to the heat dissipating fins isinstalled in the condenser. The vapor from the vapor flow passage flowsin from the inflow portion of the pipe, and refrigerant liquid from theoutflow portion of the pipe to the liquid flow passage flows out.

Patent Document 3 discloses a thermo-siphon type heat transfer body. Thespace between a heat absorbing side header block and a heat radiatingside header block, in which X-direction coolant channels and Y-directioncoolant channels are respectively formed, is connected by a plurality ofcoolant tubes. Corrugated fins are provided between the coolant tubes.In this thermo-siphon type heat transfer body, the heat absorbing sideheader block is disposed on the lower side, and the heat radiating sideheader block is disposed on the upper side, and a semiconductor elementis closely attached to the undersurface of the heat absorbing sideheader block.

Patent Document 4 discloses a liquid cooling system. A radiator isprovided in a storage container in which a heat exchange circulatingsolution and vapor thereof are stored. Moreover, a solution deliveryport and a gas-liquid two-phase fluid feeding port of the storagecontainer are coupled by a pipe of which a portion passes through thestorage container. The pipe has a solution delivery pipe portion that iscoupled to the solution delivery port and enters the storage container,an in-container pipe portion that is in the storage container, and agas-liquid two-phase fluid feeding pipe portion that comes out from thestorage container and is coupled to the gas-liquid two-phase fluidfeeding port. A heating heat exchanger that acts as a radiator for aheat-generating body such as an electronic device is provided in thegas-liquid two-phase fluid feeding pipe portion.

Patent Document 5 discloses a cooling device that is an integratedthermosiphon in which a heat receiving portion and a heat dissipatingportion are mounted in the same housing. A plurality of condenser tubesare arranged above the boiler plate, with a plurality of pyramid-shapedfins formed on the surface. Vapor chambers are constituted between thecondenser tubes and the boiler plate. In this cooling device, thecondenser tubes are sandwiched by revolving fins for heat dissipation.The vapor that is produced in the vapor chambers rises up through thecondenser tubes, and is liquefied on the walls thereof.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1]

Japanese Unexamined

Patent Application, First

Publication

-   No. 2000-183259 (FIG. 1 to FIG. 3)

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2002-168547 (FIG. 1)

[Patent Document 3] Japanese Unexamined Patent Application, FirstPublication No. 2003-166793 (FIG. 1 to FIG. 5)

[Patent Document 4] Japanese Unexamined Patent Application, FirstPublication No. 2005-195226 (FIG. 1)

[Patent Document 5] Japanese Unexamined Patent Application, FirstPublication No. 2004-056121 (FIG. 1 to FIG. 4)

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the cooling devices that are disclosed in Patent Documents 1 and 2, avapor flow passage and a liquid flow passage are installed nearlyvertical to the ceiling of the refrigerant tank, which has a thin shapeand whose ceiling is level. In such a construction, it is difficult toeffectively utilize the momentum of the vapor that is produced in therefrigerant tank to collect it in the vapor flow passage, and so thereis the problem of the vapor easily stagnating in the refrigerant tank,and the pressure loss increasing. Also, when the vapor flows verticallyupward through the vapor flow passage, the liquid phase refrigerant thathas condensed on the way tends to move downward in opposition to thevapor flow due to gravity. As a result, the pressure loss increases forthe vapor flow, and the pressure difference increases between the topand bottom of the vapor flow passage, and thereby the temperaturedifference between the top and bottom of the vapor flow passageincreases, leading to a drop in performance of the cooler. In astructure in which the vapor flow passage and the liquid flow passageopen onto the same plane of the refrigerant tank, in other words, in astructure in which the liquid flow passage opens onto the vapor space ofthe refrigerant tank, the vapor also advances to the liquid flow passageside, and thus advances in the opposite direction to the liquid that isflowing down the liquid flow passage, and so smooth flow of the coolingliquid is obstructed.

Such a problem similarly occurs in the cooling device that is disclosedin Patent Document 3, in which a heat absorbing side header block and aheat radiating side header block are connected by coolant tubes. In thecooling device that is disclosed in Patent Document 3, althoughequalization of the vapor that flows into each coolant tube is attemptedby providing coolant channels in a direction perpendicular to the headerblocks, in a structure where separation of the vapor and the liquid isnot performed, it is not a fundamental solution. The aforementionedproblem due to vapor and liquid flowing in mutually opposing directionsis not considered to occur in the cooling device of Patent Document 4,in which the flow directions of the vapor and the refrigerant solutionare the same. However, in the cooling device of Patent Document 4, thepipe portion in which only the refrigerant solution flows and the pipeportion through which a refrigerant solution that includes a largequantity of vapor are constituted by tubing of the same thickness, andthe transport capacity of the refrigerant changes greatly depending onthe portion of the pipe. For this reason, resistance arises in thecirculation of vapor after all, and there is a possibility that thesmooth circulation of vapor may be impeded. Also, although many of thecomponents that are cooled are plate shaped, in the cooling device ofPatent Document 4, the heat absorbing portion is a pipe body. For thisreason, since contact between the heat absorbing portion of the coolingdevice and the component being cooled is not surface contact, thermalresistance there between increases, and so it becomes difficult toperform efficient cooling.

The aforementioned problem of vapor pressure loss does not occur in thestructure disclosed in Patent Document 5 in which an evaporating portionand a condensing portion are unified. Due to it having a condensingportion directly above the evaporation surface, circulation of therefrigerant between the evaporating portion and the condensing portionis performed efficiently. However, the manufacture of an integratedconstitution is difficult and costly, and such a constitution is flawedin terms of efficient heat dissipation as described below. If theboiling heat transfer device that is used for cooling of an electricalcomponent (heat generating body) can radiate heat in the vicinity of thecomponent, the possibility of being able to minimize the pressure lossincreases from the standpoint of circulation of the refrigerant. On theother hand, in the case of bring the heat absorbing portion and heatdissipating portion in close proximity as in the boiling heat transferdevice disclosed in Patent Document 5, thermal isolation of the heatabsorbing portion and the heat dissipating portion becomes difficult,and so it becomes difficult to efficiently perform heat dissipation fromthe heat dissipating portion to the outside.

The issue of the present invention is to solve the aforementionedproblems of the conventional art, and it has as its object to provide aboiling heat transfer device that is capable of both the functions ofincreasing the heat dissipation to the outside of the device to themaximum and suppressing the pressure loss of the refrigerant circulationsystem to a low level, which until now have been regarded as opposingconcepts.

Means for Solving the Problem

In order to achieve the aforementioned objects, a boiling heat transferdevice according to a first aspect of the present invention includes: aheat receiving portion that boils a liquefied refrigerant to convert itto vapor, and contacts with a device to be cooled and cools the deviceto be cooled; a vapor tube that connects to an upper portion of the heatreceiving portion and conveys the vapor generated by the heat receivingportion; a heat dissipating portion that condenses the vapor conveyedfrom the vapor tube to convert it to a liquefied refrigerant anddissipates heat to an atmosphere; and a liquid tube that returns to theheat receiving portion the liquefied refrigerant condensed by the heatdissipating portion, and at least a portion of a cross-sectional area ofa flow passage of the vapor in the heat receiving portion graduallydecreases from a lower portion of the heat receiving portion toward theupper portion of the heat receiving portion.

Also, in order to achieve the aforementioned objects, a boiling heattransfer device according to a second aspect of the present inventionincludes: a heat receiving portion that boils a liquefied refrigerant toconvert it to vapor, and contacts with a device to be cooled and coolsthe device to be cooled; a vapor tube that conveys the vapor generatedby the heat receiving portion; a heat dissipating portion that condensesthe vapor conveyed from the vapor tube to convert it to a liquefiedrefrigerant and dissipates heat to an atmosphere; and a liquid tube thatreturns to the heat receiving portion the liquefied refrigerantcondensed by the heat dissipating portion, and the vapor tube is drawnout from the heat receiving portion side in a parallel direction to adirection of gravity, and is bent in a direction close to horizontaltoward the heat dissipating portion.

Effect of the Invention

The first effect of an exemplary embodiment of the present invention isto be able to reduce to the utmost the pressure loss of the circulationsystem of an entire boiling heat transfer device.

The second effect of the exemplary embodiment of the present inventionis to be able to prevent back flow of the condensed refrigerant in thevapor tube while making use of the advantage of the decoupled system inwhich direct heat dissipation is possible with respect to outside of thecooling apparatus by separating the heat dissipating portion from theheat receiving portion in a decoupled boiling heat transfer device thatseparates the heat receiving portion and the heat dissipating portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view that shows a boiling heat transfer deviceaccording to a first exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view that shows a heat receiving portion ofthe first exemplary embodiment of the present invention.

FIG. 3A is a side view that shows a heat dissipating portion of thefirst exemplary embodiment of the present invention.

FIG. 3B is a cross-sectional view along line A-A in FIG. 3A.

FIG. 4A is a view that shows a typical vertical-type vapor tube thatconnects a heat receiving portion and a heat dissipating portion.

FIG. 4B is view that shows a horizontal transition-type vapor tube thatconnects the heat receiving portion and the heat dissipating portion inthe first exemplary embodiment of the present invention.

FIG. 5A is a transverse cross-sectional view that shows a heat receivingportion of a second exemplary embodiment of the present invention.

FIG. 5B is a vertical cross-sectional view that shows the heat receivingportion of the second exemplary embodiment of the present invention.

FIG. 6A is a transverse cross-sectional view that shows a heat receivingportion of a third exemplary embodiment of the present invention.

FIG. 6B is a vertical cross-sectional view that shows the heat receivingportion of the third exemplary embodiment of the present invention.

FIG. 7 is a cross-sectional view that shows a heat receiving portion ofa fourth exemplary embodiment of the present invention.

FIG. 8 is a view that shows an example of a porous material that is usedin the heat receiving portion of the fourth exemplary embodiment of thepresent invention.

FIG. 9 is a view that shows another example of a porous material that isused in the heat receiving portion of the fourth exemplary embodiment ofthe present invention.

FIG. 10 is a cross-sectional view that shows the heat receiving portionof the fifth exemplary embodiment of the present invention.

FIG. 11A is a plan view of a bottom plate that has a square shape.

FIG. 11B is a cross-sectional view along line A-A of FIG. 11A.

FIG. 11C is a plan view of a bottom plate that has a circular shape.

FIG. 11D is a cross-sectional view along line A-A of FIG. 11C.

FIG. 12A is a plan view of a side wall portion with a square shape.

FIG. 12B is a cross-sectional view along line A-A of FIG. 12A.

FIG. 12C is a plan view of a side wall portion with a circular shape.

FIG. 12D is a cross-sectional view along line A-A of FIG. 12C.

FIG. 13A is a plan view of a cover portion with a circular plate shape.

FIG. 13B is a cross-sectional view of the cover portion with thecircular plate shape.

FIG. 13C is a plan view of a cover portion with a truncated cone shape.

FIG. 13D is a cross-sectional view of the cover portion with thetruncated cone shape.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Next, exemplary embodiments of the present invention shall be describedin detail with reference to the drawings.

First Exemplary Embodiment

FIG. 1 is a schematic view that shows a boiling heat transfer deviceaccording to a first exemplary embodiment of the present invention. Theboiling heat transfer device has a heat receiving portion 1, a vaportube 2, a heat dissipating portion 3, a liquid tube 4, a cooling fan 6,and a refrigerant pouring inlet 7. The upper portion of the heatreceiving portion 1 and the upper portion of the heat dissipatingportion 3 are connected by the vapor tube 2. The liquid tube 4 that isdrawn out from the bottom of the heat dissipating portion 3 is connectedto the side of the heat receiving portion 1. The cover portion of theheat receiving portion 1 has a pyramid shape. The vapor tube 2 that isdrawn out vertically from the top of the heat receiving portion 1 isbent in a circular arc and connected to the heat dissipating portion 3in a horizontal state. That is, the vapor tube 2 has a first end portionthat is connected to the heat receiving portion 1 and a second endportion 2 that is connected to the heat dissipating portion 3. Theorientation of the center axis of the vapor tube 2 is approximatelyparallel with respect to the direction of gravity in the vicinity of thefirst end portion. The orientation of the center axis of the vapor tube2 is approximately perpendicular to the direction of gravity in thevicinity of the second end portion. The bottom surface of the heatreceiving portion 1 is flat. At the bottom surface of the heat receivingportion 1, a heat generating element 5 such as a semiconductor device isarranged in close contact. The refrigerant pouring inlet 7 is providedat the upper portion of the heat dissipating portion 3 for initialfilling of the refrigerant and topping up of the refrigerant. Thecooling fan 6 for cooling the heat dissipating portion 3 is installed onthe side of the heat dissipating portion 3.

The refrigerant boils inside of the heat receiving portion 1 that facesthe heat generating element 5, and the vapor that is thereby generatedheads to the outlet to the vapor tube 2. The heat receiving portion 1 isformed so that the vapor flow passage gradually narrows toward the vaportube 2. The vapor tube 2 opens at a position directly above the heatgenerating element 5. By this structure, the force of the flow of theboiling bubbles is effectively utilized, and so the vapor that isgenerated at the heat receiving portion 1 is guided to the vapor tube 2with low resistance. By gently changing the angle of the vapor tube 2,the vapor is carried toward the heat dissipating portion 3 in thedirection of the arrow 8. The fact that the vapor tube 2 is connected tothe upper side of the condenser 3 is considered to be a good conditionfor ensuring the performance of the heat dissipating portion 3. Thevapor that is guided to the heat dissipating portion 3 flows from thetop to the bottom inside of the heat dissipating portion 3, and returnsto liquid. The refrigerant that has returned to liquid collects at thebottom of the heat dissipating portion 3, moves through the liquid tube4 in the direction of the arrow 9, and returns to the heat receivingportion 1.

FIG. 2 is a cross-sectional view of the heat receiving portion 1. Theheat receiving portion 1 has a main body 1 a, a vapor outflow portion 1c, a cover portion 1 b, and a condensate inflow portion 1 d. The mainbody portion 1 a has a box shape, and the flat surfaces thereof form asquare. The cover portion 1 b has a pyramid shape, and is providedbetween the main body portion 1 a and the vapor outflow portion 1 c. Thecondensate inflow portion 1 d is formed on the side of the main bodyportion 1 a. The liquid phase refrigerant 11 that has returned from thecondenser (heat dissipating portion 3) flows in from the side of theheat receiving portion 1 via the condensate inflow portion 1 d. Arefrigerant liquid 12 collects inside of the heat receiving portion 1.The refrigerant liquid 12 boils from the heat of the heat generatingelement 5 such as an electronic device that is installed at the bottomof the heat receiving portion 1, and produces boiling bubbles 13. Avapor 10 that is generated flows out to the vapor tube 2 from the vaporoutflow portion 1 c above. Comparing the tube diameter of the liquidtube 4 for the liquid phase refrigerant and the vapor tube 2 for thevapor phase, the tube diameter of the vapor tube 2 is set to be larger.When the entire cooler is in a steady state, the mass-base flow amountis same everywhere, but the volumetric-base flow amount differs greatly.This is due to the density of the liquid and vapor changing greatly. Thesmall diameter of the liquid tube 4 that is connected to the heatreceiving portion 1 has the effect of preventing the mixing in of thevapor. Accordingly, in the present exemplary embodiment, it is mostpreferred that the heat receiving portion 1 have a structure of beingconnected with the small-diameter liquid tube 4 that is connected to theside of the heat receiving portion 1 and to the comparatively largerdiameter vapor tube 2 that is connected to the upper portion of the heatreceiving portion 1. With this structure, in conjunction with theliquid-phase back-flow preventive measure in the vapor tube 2 describedbelow, it is possible to realize without a check valve a system that canprevent back flow or, even if back flow occurs, can suppress to aminimum the effect thereof.

FIG. 3A is a side view that shows the structure of the heat dissipatingportion 3 in the present exemplary embodiment. FIG. 3B is a side viewalong line A-A in FIG. 3A. The heat dissipating portion 3 has a heatdissipating portion header 3 a, a condensate collection portion 3 b,vapor-condensate cylinders 3 c, vapor-condensate flow passages 3 c′,heat dissipating fins 3 d, a vapor flow inlet 3 e, a condensate outlet 3f, and a frame 3 g.

The vapor flow inlet 3 e is fixed to the heat dissipating portion header3 a. The condensate outlet 3 f is fixed to the condensate collectionportion 3 b. The heat dissipating portion header 3 a and the condensatecollection portion 3 b are connected by the vapor-condensate pipe 3 c.The vapor-condensate flow passage 3 c′ is formed inside of thevapor-condensate pipe 3 c, and vapor and condensate flow through it. Theheat dissipating fin 3 d is installed between the frame 3 g and thevapor-condensate cylinder 3 c, and between the vapor-condensatecylinders 3 c. The vapor that has flowed in from the vapor tube 2 to theheat dissipating portion header 3 a via the vapor flow inlet 3 e isdispersed to the left and right (that is, in the direction of the arrowsin FIG. 3B) upon abutting a surface opposing the surface at which thevapor flow inlet 3 e is provided. Thereby, the vapor can be made tospread throughout the entire header 3 a. Thereafter, the vapor condenseswhile passing through the vapor-condensate flow passages 3 c′. At thistime, the liquefied refrigerant heads toward the condensate collectionportion 3 b due to gravity. The vapor-condensate pipes 3 c make contactwith the heat dissipating fins 3 d, and so heat is dissipated to theatmosphere by the air that passes between the fins 3 d. Condensation isperformed on the inner wall of the vapor-condensate flow passages 3 c′.An effect of promoting the operation is achieved when the flow passageinner wall is hindered from being covered by a condensate film. As onemethod of doing so, a method is conceivable that involves applying awater repellent treatment to the inner wall surface, but itseffectiveness with respect to a refrigerant that has a high wetness isnot high. For that reason, one of the best methods is to form therefrigerant flow passage in a state close to vertical, and discharge therefrigerant to the condensate collection portion 3 b using gravity. Therefrigerant pouring inlet 7 is provided in the heat dissipating portion3. When pouring in the refrigerant, it is necessary to removenoncondensable gas in the boiling heat transfer device at the same time.Since gas has a lower density compared to the refrigerant liquid, it isnecessary to suction it from above in the direction of gravity. Where toinstall this refrigerant pouring inlet 7 therefore becomes an issue. Itis optimal to install the refrigerant pouring inlet 7 at a position thatexerts little effect on the refrigerant circulation after sealing theboiling heat transfer device. Therefore, when the refrigerant pouringinlet 7 is provided in a corner portion of the heat dissipating portionheader 3 a, exhaust of the noncondensable gas can be effectivelyperformed, and it is possible to minimize the effect exerted on the flowof the vapor after sealing.

Referring to FIG. 4A and FIG. 4B, the action/effect of the vapor tube 2that is used in the present exemplary embodiment being bent in thehorizontal direction after being drawn out in the vertical directionshall be described. FIG. 4A shows the method generally used to connectedthe heat receiving portion 1 and the heat dissipating portion 3 with thevertical vapor tube 2. As shown in FIG. 4A, since the vapor tube 2 isentirely arranged vertically, by utilizing the lift of the vapor, it isconsidered possible to cause the vapor to efficiently move along thearrow 8 that shows the vapor flow direction until the heat dissipatingportion 3 (condenser portion). Also, since the vapor tube 2 is not bent,there is the appeal of the pressure loss caused by that being small.However, the vapor that comes into contact with the inner wall of thevapor tube 2 may condense, and the refrigerant that thus liquefiesstarts to flow downward along the inner wall in the direction of thearrow 9, and tries to return to the heat receiving portion 1. At thistime, since it flows in the opposite direction to the flow of the vapor,resistance arises for both the vapor and the condensate. As a result,the pressure loss for the vapor increases, there is the risk of a largepressure loss inducing more condensation in the tube. Accordingly, thereis the fear of the flow of the system becoming unstable in the case of alot of vapor being produced in a high heat generation state. Next, asshown in FIG. 4B, a method of connecting the heat receiving portion 1and the heat dissipating portion 3 by the vapor tube 2 having the shapeof a circular arc (horizontal transition-type) shall be considered. Whenconsidering the case of the length of the vapor tube 2 being equivalentso that the pressure loss in the state of condensation not occurringbeing the same in order to compare with the case of the vertical-typevapor tube 2, there is a possibility of condensation itself occurringwithin the horizontal transition-type vapor tube 2 shown in FIG. 4B.However, the vapor tube 2 has a structure in which the latter half (theheat dissipating portion 3 side of the vapor tube 2) extends in a stateclose to horizontal. For this reason, even in the case of a portion ofthe vapor having condensed in the latter half of the vapor tube 2, theliquefied refrigerant is pushed by the vapor flow that moves in thedirection of arrow 8 and thereby sent to the condenser in the directionof the arrow 9, so that its return to the vaporizing portion iseliminated. At the same temperature, condensation more readily occurs ata lower pressure. Inside of the vapor tube 2, since the pressuredecreases from the entrance on the side of the heat receiving portion 1to the exit on the side of the heat dissipating portion 3 due to theflow, condensation usually begins from close to the exit. For thatreason, preventing back flow of the liquid phase that condenses near theexit of the vapor tube 2 greatly contributes to stable operation of thesystem.

Second Exemplary Embodiment

FIG. 5A is a transverse cross-sectional view that shows a heat receivingportion of a second exemplary embodiment of the present invention. FIG.5B is a vertical cross-sectional view that shows the heat receivingportion of the second exemplary embodiment of the present invention. Inthe heat receiving portion shown in FIG. 5A and FIG. 5B, the samereference symbols are given to the same locations as the heat receivingportion of the first exemplary embodiment shown in FIG. 2, and sooverlapping descriptions are omitted. In the present exemplaryembodiment, a plurality of boiling promotion fins (also called boilingpromotion plates, or simply fins) 14 are provided on the inside bottomsurface of the main body portion 1 a of the heat receiving portion 1.Thereby, it is possible to increase the contact surface area to theliquid phase of the boiling surface, and it is possible to raise theefficiency of heat reception. The arrows 16 show the direction of theliquid flow. The arrow 17 shows the direction of the vapor flow. Afterthe liquid-phase refrigerant 11 has flown in to the heat receivingportion 1, it flows in between the boiling promotion fins 14 that areformed along the flow as shown by the arrows 16. Also, since the boilingpromotion fins 14 are provided, flows of the refrigerant between theboiling promotion fins 14 are formed. Also, during the rise of theboiling bubbles, the bubbles flow between the boiling promotion fins 14with vigor, and so the heat transmission is promoted by the convectiveeffect.

Third Exemplary Embodiment

FIG. 6A is a transverse cross-sectional view that shows a heat receivingportion of a third exemplary embodiment of the present invention. FIG.6B is a vertical cross-sectional view that shows the heat receivingportion of the third exemplary embodiment of the present invention. Inthe heat receiving portion shown in FIG. 6A and FIG. 6B, the samereference symbols are given to the same locations as the heat receivingportion of the second exemplary embodiment shown in FIG. 5A and FIG. 5B,and so overlapping descriptions are omitted. In the present exemplaryembodiment, as shown in FIG. 6A, the planar shape of the heat receivingportion 1 is oval. Since the main body portion 1 a of the heat receivingportion 1 has an oval shape, the cover portion 1 b has the shape of anelliptical truncated cone. Due to the heat receiving portion 1 having anoval shape, the flow of the vapor is smoother. The planar shape of theheat receiving portion 1 may be circular instead of oval, and it ispossible to select a suitable shape in accordance with the shape of theheat generating element 5 that is to be cooled.

Fourth Exemplary Embodiment

FIG. 7 is a vertical cross-sectional view that shows a heat receivingportion of a fourth exemplary embodiment of the present invention. Inthe heat receiving portion of FIG. 7, the same reference symbols aregiven to the same locations as the heat receiving portion of the secondexemplary embodiment shown in FIG. 5A and FIG. 5B, and so overlappingdescriptions are omitted. In the present exemplary embodiment, theboiling promotion fins 14 that promote boiling of the refrigerant areformed using a porous material. In the case of using porous fins, thefoam amount from the holes increases, and so the heat transmissionamount also improves. FIG. 8 shows a magnified view of Full Porous(product name) manufactured by Furukawa-Sky Aluminum Corp. as oneexample of a porous material. Also, FIG. 9 shows a magnified view ofAlporas (product name) manufactured by Shinko Wire Co. as anotherexample. These are both porous materials made of aluminum. Thesematerials can be favorably used for the boiling promotion fins 14.

Fifth Exemplary Embodiment

FIG. 10 is a vertical cross-sectional view that shows a heat receivingportion of a fifth exemplary embodiment of the present invention. In theheat receiving portion of FIG. 10, the same reference symbols are givento the same locations as the heat receiving portion of the secondexemplary embodiment shown in FIG. 5A and FIG. 5B, and so overlappingdescriptions are omitted. In the case of the heat receiving portion ofthe second exemplary embodiment shown in FIG. 5A and FIG. 5B, theconnection portion at each portion of the heat receiving portion isabruptly bent at a certain angle. In this case, there is the possibilityof pressure loss occurring due to the flow that wraps around the anglenot being able to conform to the shape of angle. The present exemplaryembodiment addresses this, and as shown in FIG. 10, the main bodyportion 1 a and the cover portion 1 b of the heat receiving portion, andthe cover portion 1 b and the vapor outflow portion 1 c are joined sothat the angles therebetween draw a smooth line. That is, the connectionportion between the main body portion 1 a and the cover portion 1 binside of the heat receiving portion 1 is formed with a streamlinedform. Also, the connection portion between the cover portion 1 b and thevapor outflow portion 1 c inside of the heat receiving portion 1 isformed with a streamlined form. By adopting such a shape, sudden changesin the flow are prevented, and so the flow of the vapor becomessmoother, whereby it is possible to minimize flow pressure loss.

Action of the Exemplary Embodiment of the Present Invention

According to the boiling heat transfer device of the exemplaryembodiments of the present invention, in the heat receiving portion 1,the refrigerant evaporates, and the vapor that occurs from the boilingflows upward in the reverse direction of gravity due to the lift. Thevapor tube 2 is connected to the upper portion of the heat receivingportion 1. The refrigerant vapor is sent to the heat dissipating portion(heat exchange portion) 3 through the vapor tube 2 without impairing themomentum of the vapor that is produced by the lift. In the heatdissipating portion 3, heat is removed from the refrigerant, and therefrigerant is liquefied and condensed. The liquid refrigerant that hascondensed returns from the bottom of the heat dissipating portion 3 tothe liquid refrigerant of the heat receiving portion (boiling portion) 1through the liquid tube 4.

The outer bottom surface of the heat receiving portion 1 of the boilingheat transfer device of the exemplary embodiments of the presentinvention is formed in a planar shape, and the boiling surface that isthe inner bottom surface thereof is formed in a planar shape. The heatreceiving portion 1 is capable of boiling and heat reception byutilizing the entire surface of a semiconductor package. While aconventional heat pipe has a heat receiving structure on the sidesurface of a circular or oval pipe, the heat receiving structure of theexemplary embodiments of the present invention is capable oftransmitting heat in a superior manner. Also, the planar shape heatreceiving structure is superior also in terms of constructing astructure that promotes the gas phase change of the refrigerant byefficiently transmitting the heat from the package to the refrigerant.The boiling bubbles that are produced at the planar boiling surface flowupward with a given speed in the opposite direction to the direction ofgravity. As the cross sectional area of the vapor tube (tube) 2 that isconnected to the heat dissipating portion 3 is small compared to thearea of the boiling surface, it is possible to make the overall size ofthe boiling cooling device compact. In order to circulate the flow ofvapor bubbles that are produced to the vapor tube 2 in an efficientmanner, the side walls of the upper portion of the heat receivingportion 1 have the shape of a truncated cone or a truncated pyramid sothat the cross-sectional area of the vapor flow passage graduallydecreases. For that reason, it is possible to minimize the pressure lossfrom the boiling surface to the vapor tube 2.

Moreover, the vapor tube 2 is bent from immediately after the connectionportion with the heat receiving portion 1 in a lateral direction respectto the direction of gravity, and is sent to the heat dissipating portion(condenser) 3. The heat dissipating portion 3 and the heat receivingportion 1 are installed in a lateral direction with respect to thedirection of gravity. Even in the event of condensation having occurredinside of the vapor tube 2, the liquid-state refrigerant is sent to theheat dissipating portion 3 along the flow of the vapor (refer to FIG.4B), and so it is possible to inhibit its accumulation in the vapor tube2.

In the heat dissipating portion 3, the portion where the vapor tube 2reaches by being bent serves as the upper entry, and the condensedliquid phase circulated to the heat receiving portion 1 from the lowerportion of the heat dissipating portion 3. At that time, the liquefiedrefrigerant from the heat dissipating portion 3 is discharged into theliquefied refrigerant in the heat receiving portion (boiling portion) 1.Thereby, mixing of vapor into the liquefied refrigerant that is flowingback is prevented. The liquid-phase return flow to the heat receivingportion 1 from the heat dissipating portion 3 depends on the flow due togravity. In the boiling heat transfer device of the exemplaryembodiments of the present invention, making the difference of elevationsmall keeps the pressure difference small. Thereby, it is possible tofurther reduce the pressure loss. As shown in FIG. 1 and FIG. 2, theheight of the bottom surface in the heat dissipating portion 3 isslightly higher than the height of the liquid surface of liquefiedrefrigerant in the heat receiving portion 1. Due to this heightdifference, return flow of the liquefied refrigerant to the heatreceiving portion 1 becomes possible. [Supplementary Description ofStructure and Manufacturing Method]

Next, a supplementary description of the preferred structure of theboiling heat transfer device of the aforementioned exemplary embodimentsof the present invention and an outline description of the manufacturingmethod shall be given.

A description shall be given for the heat receiving portion shown inFIG. 2, FIG. 5A, and FIG. 7. The main body portion 1 a of the heatreceiving portion 1 is constituted by a bottom plate 1 a ₁ and a sidewall portion 1 a ₂. FIG. 11B is a cross-sectional view along line A-A ofFIG. 11A. FIG. 11C is a plan view of the bottom plate 1 a ₁ in the caseof the bottom plate being round. FIG. 11D is a cross-sectional viewalong line A-A of FIG. 11C. FIG. 12A is a plan view of the side wallportion 1 a ₂ in the case of the side wall portion being square. FIG.12B is a cross-sectional view along line A-A in FIG. 12A. FIG. 12C is aplan view of the side wall portion 1 a ₂ in the case of the side wallportion being round. FIG. 12D is a cross-sectional view along line A-Aof FIG. 12C. FIG. 13A and FIG. 13B are a plan view and cross-sectionalview, respectively, of the cover portion 1 b in the case of the coverportion being a circular plate. FIG. 13C and FIG. 13D are a plan viewand a cross-sectional view, respectively, of the cover portion 1 b inthe case of the shape of the cover portion having the shape of atruncated cone.

Since the bottom plate 1 a ₁ of the heat receiving portion 1 is incontact with the heat generating element 5, it is preferable to use amaterial with a high thermal conductivity. In particular, as thematerial of the bottom plate 1 a ₁, a general purpose metal having ahigh thermal conductivity such as copper or aluminum is preferable. Itis preferred to use this material to form it in an integrated mannerfrom the surface that is in contact with the heat generating element 5(lower surface of the bottom plate 1 a ₁) to the boiling promotion fins14 that generate the boiling bubbles. In the boiling promotion fins 14,the first object is to generate boiling bubbles, and so it is necessaryto efficiently discharge the vapor while supplying the liquid that isrequired to always continue the boiling. When an organic refrigerant isused, generally the surface tension is less than water, and so thediameter of bubbles that form at the time of boiling is around 1.0 mm.In such a case, it is not desirable to make the distance between theboiling promotion fins 14 extremely narrow to be less than the bubblediameter, and it is preferable that it be equal to or greater than thebubble diameter. On the other hand, in consideration of the fact that itis possible to also increase the heat discharge amount as the surfacearea of the boiling promotion fins 14 becomes wider, when the distancebetween the boiling promotion fins 14 becomes too great, the number ofboiling promotion fins 14 that can be formed becomes limited. Moreover,the quantity of heat that passes through the inside of the boilingpromotion fins 14 depends on the thickness of the boiling promotion fins14. The thicker the boiling promotion fins 14, the more heat that flows,but when they are made excessively thick, the heat dissipation surfacearea is limited. In consideration of these points, the optimal structureof the boiling promotion fins 14 is for the distance between the fins tobe 1.0 mm, the fin thickness to be 1.0 to 2.0 mm, and the fin height tobe 1.0 to 5.0 mm. In the case of a fin structure with an aspect ratio ofaround 1:5 in these millimeter scales, manufacturing by machining is oneof the favorable methods. When the boiling promotion fins 14 and thebottom plate 1 a ₁ in the heat receiving portion 1 are integrallyformed, it is possible to reduce the thermal resistance that occurs inthe connection portions thereof compared to the case of forming themseparately and combining them. FIGS. 11A to 11D show an example of thecase of the boiling promotion fins 14 and the bottom plate 1 a ₁ beingintegrally formed.

In the case of forming the boiling promotion fins 14 using the porousmaterial shown in FIG. 7, a method that makes the bottom surface of thebottom plate 1 a ₁ smooth, and joins the porous material to the smoothedbottom surface by brazing or the like is preferred. The porous materialsthat are exemplarily shown in FIG. 8 and FIG. 9 are both made ofaluminum, and in this case it is preferable to also use the samealuminum for the bottom plate 1 a ₁.

A method of manufacturing the heat receiving portion shall be describedusing FIG. 12A to FIG. 12D. The side wall portion 1 a ₂ is made using amaterial with high thermal conductivity (copper or aluminum). Thecondensate inflow portion 1 d, on which a screw thread is formed, isscrewed into the side wall portion 1 a ₂. Next, the bottom plate 1 a ₁and the side wall portion 1 a ₂ are joined by a means such as brazing toform the main body portion 1 a of the heat receiving portion 1. Thecover portion 1 b shown in FIGS. 13A to 13D that is formed using amaterial similarly having high thermal conductivity is joined with themain body portion 1 a by a means such as brazing or the like to form theheat receiving portion 1. As shown in FIG. 13A and FIG. 13B, the vaporoutflow portion 1 c, on which a screw thread is formed in advance, isscrewed into the cover portion 1 b. Alternatively, the cover portion 1 bmay be integrally formed in advance with the vapor outflow portion 1 cas shown in FIG. 13C and FIG. 13D. By joining each portion by brazing,it is possible to obtain the heat receiving portion 1 having a sealedstructure that is capable of withstanding pressure fluctuations duringboiling.

The heat dissipating portion 3 is constituted mainly by a heatdissipating portion header 3 a, a condensate collection portion 3 b, avapor-condensate cylinder 3 c, and a heat dissipating fin 3 d. Thisbasic structure resembles a radiator that is used in an automobile orthe like. However, in the exemplary embodiment of the present invention,since condensation of the refrigerant vapor is performed in addition tothe heat dissipation, it is essential to be able to perform efficientheat dissipation in the condensation of the refrigerant. As shown in thecross-sectional view of FIG. 3B, connecting the vapor flow inlet 3 e ina perpendicular manner near the center of the heat dissipating portionheader 3 a is favorable. As a result, the vapor that flows into the heatdissipating portion header 3 a collides with the wall on the backsurface side of the heat dissipating portion header 3 a, and it ispossible to cause it to disperse so as to permeate the heat dissipatingportion header 3 a. Thereby, it is possible to make the pressure insideof the heat dissipating portion header 3 a stable, and accordingly it ispossible to make the flow rates of the vapor-condensate flow passages 3c′ uniform.

From the standpoint of heat dissipation, the narrower that thevapor-condensate cylinder 3 c is, the better, but from the standpoint ofthe flow of the condensed refrigerant, a certain degree of thickness isrequired. In the exemplary embodiment of the present invention,condensation relies on the liquid phase exclusion capability, whichdepends on gravity. Ideally, the condensed refrigerant forms a thin-filmliquid phase on the inner wall of the flow passage of thevapor-condensate cylinder 3 c, and is discharged to the condensatecollection portion 3 b side by gravity. In rare cases, the vapor becomesbubbles in the condensed liquid phase and becomes trapped, and in such acase, it serves as resistance to the discharge of the liquid phase. Inorder to avoid such a situation, the flow passage width of thevapor-condensate cylinder 3 c should be the minimum. In the case ofusing an organic refrigerant, the width of the inner surface of the flowpassage of the vapor-condensate cylinder 3 c is 0.3 mm or more, and fromthe standpoint of heat dissipation, the width of the inner surface ofthe flow passage of the vapor-condensate cylinder 3 c is preferably 1.0mm or less.

It is preferable to use a flexible tubing material in the connectionbetween the heat receiving portion 1 and the heat dissipating portion 3.A polymer material has high flexibility, but is also permeable, and sothe refrigerant may leak out through the tubing wall surface. In orderto realize a flexible connection, use of a material such as butyl rubberwhich, although it is a polymer, has low permeability, use of a polymertubing material in which a metallic thin film is laminated, and adoptionof a metal tubing material that maintains flexibility with a bellowsshape, etc. is favorable.

It is preferable to provide an inflow/outflow nozzle at the positionsthat connect the tubing to the heat receiving portion 1 and the heatdissipating portion 3, and connect the tubing material to them. Sincethere is a risk of leakage of the refrigerant through surface boundaryof the connection portions and the tubing material, it is preferable toseal the connection portions using an adhesive material.

When the sealing of the connection portions is finished, the refrigerantis poured in through the refrigerant pouring inlet 7, and removal ofincluded air is performed. Removing the air leads to the saturationvapor pressure of the refrigerant inside of the cooler. As one conditionof refrigerant selection, the saturation vapor pressure is preferably asclose to 1 atm as possible. This because it is necessary to increase thestrength of the cooler for one that greatly deviates from 1 atm. Forexample, Novec, one type of fluorinated refrigerant manufactured by 3MCompany, has a boiling point at an atmospheric pressure of 47° C., and asaturation vapor pressure at room temperature of approximately 40 kPa.In consideration of the cooling electronic equipment, the differencefrom atmospheric pressures at room temperature is not so large, andsince during operation it is possible to keep it below 2 atm or less,this refrigerant is favorable in a boiling and cooling apparatusaccording the exemplary embodiments of the present invention.

Hereinabove, while the invention has been particularly shown anddescribed with reference to exemplary embodiments thereof, the inventionis not limited to these embodiments. It will be understood by those ofordinary skill in the art that various changes in form and details maybe made therein without departing from the scope of the presentinvention as defined by the claims.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2008-294282, filed on Nov. 18, 2008, thedisclosure of which is incorporated herein in its entirety by reference.

INDUSTRIAL APPLICABILITY

It is possible to apply the present invention to a boiling heat transferdevice. According to this boiling heat transfer device, it is possibleto achieve a function that suppresses pressure loss of the refrigerantcirculation system to a low level while raising the heat dissipation tooutside the device to a maximum level.

REFERENCE SYMBOLS

1 Heat receiving portion

1 a Main body portion

1 a ₁ Bottom plate

1 a ₂ Side wall portion

1 b Cover portion

1 c Vapor outflow portion

1 d Condensate inflow portion

2 Vapor tube

3 Heat dissipating portion

3 a Heat dissipating portion header

3 b Condensate collection portion

3 c Vapor-condensate cylinder

3 c′ Vapor-condensate flow passage

3 d Heat dissipating fin

3 e Vapor flow inlet

3 f Condensate outlet

3 g Frame

4 Liquid tube

5 Heat generating element

6 Cooling fan

7 Refrigerant pouring inlet

8 Arrow (vapor flow direction)

9 Arrow (liquid flow direction)

10 Vapor (vapor-phase refrigerant)

11 Liquid-phase refrigerant

12 Refrigerant

13 Boiling bubble

14 Boiling promotion fin

15 Vapor flow direction

16 Arrow (liquid flow direction)

17 Arrow (vapor fl0w direction)

1. A boiling heat transfer device comprising: a heat receiving portionthat boils a liquefied refrigerant to convert it to a vapor, andcontacts with a device to be cooled and cools the device to be cooled; avapor tube that connects to an upper portion of the heat receivingportion and conveys the vapor generated by the heat receiving portion; aheat dissipating portion that condenses the vapor conveyed from thevapor tube to convert it to a liquefied refrigerant and dissipates heatto an atmosphere; and a liquid tube that returns to the heat receivingportion the liquefied refrigerant condensed by the heat dissipatingportion, at least a portion of a cross-sectional area of a :flow passageof the vapor in the heat receiving portion gradually decreasing from alower portion of the heat receiving portion toward the upper portion ofthe heat receiving portion.
 2. The boiling heat transfer deviceaccording to claim 1, wherein the vapor tube is drawn out from the heatreceiving portion side in a parallel direction to a direction ofgravity, and is bent in a direction close to horizontal toward the heatdissipating portion.
 3. The boiling heat transfer device according toclaim 1, wherein the vapor tube has a first end portion connected withthe heat receiving portion and a second end portion connected with theheat dissipating portion, and an orientation of a center axis of thevapor tube is approximately parallel to a direction of gravity in avicinity of the first end portion and approximately perpendicular to thedirection of gravity in a vicinity of the second end portion.
 4. Aboiling heat transfer device comprising: a heat receiving portion thatboils a liquefied refrigerant to convert it to vapor, and contacts witha device to be cooled and cools the device to be cooled; a vapor tubethat conveys the vapor generated by the heat receiving portion; a heatdissipating portion that condenses the vapor conveyed from the vaportube to convert it to a liquefied refrigerant and dissipates heat to anatmosphere; and a liquid tube that returns to the heat receiving portionthe liquefied refrigerant condensed by the heat dissipating portion, thevapor tube being drawn out from the heat receiving portion side in aparallel direction to a direction of gravity and being bent in adirection close to horizontal toward the heat dissipating portion. 5.The boiling heat transfer device according to claim 3, wherein the vaportube starts to bend immediately after a connection portion with the heatreceiving portion.
 6. The boiling heat transfer device according toclaim 1, where in the heat receiving portion and the heat dissipatingportion are installed in a lateral direction with respect to a directionof gravity.
 7. A boiling heat transfer device comprising: a heatreceiving portion that boils a liquefied refrigerant to convert it tovapor, and contacts with a device to be cooled and cools the device tobe cooled; a vapor tube that conveys the vapor generated by the heatreceiving portion; a heat dissipating portion that condenses the vaporconveyed from the vapor tube to convert it to a liquefied refrigerantand dissipates heat to an atmosphere; and a liquid tube that returns tothe heat receiving portion the liquefied refrigerant condensed by theheat dissipating portion, height of a liquid surface of the liquefiedrefrigerant in the heat receiving portion being higher than height of abottom surface of the heat dissipating portion.
 8. The boiling heattransfer device according to claim 1, wherein the liquid tube is drawnout from a bottom portion of the heat dissipating portion, and theliquefied refrigerant that passes through the liquid tube is directlyreturned to the liquefied refrigerant in the heat receiving portion. 9.The boiling heat transfer device according to claim 1, wherein the heatreceiving portion has a main body portion that has a box shape and acover portion that covers the main body portion, and an outer shape ofthe cover portion is a truncated cone or a truncated pyramid.
 10. Theboiling heat transfer device according to claim 1, wherein the device tobe cooled is disposed in a center portion directly below the heatreceiving portion, and the vapor tube opens at an upper center of theheat receiving portion.
 11. The boiling heat transfer device accordingto claim 1, wherein at least one of a connection portion between a vaporoutflow portion of the heat receiving portion and a main body portion ofthe heat receiving portion, and a connection portion between the mainbody portion of the heat receiving portion and the cover portion of theheat receiving portion is formed in a streamlined shape.
 12. The boilingheat transfer device according to claim 1, wherein a plurality ofboiling promotion fins are provided in the heat receiving portion. 13.The boiling heat transfer device according to claim 12, wherein theboiling promotion fins include a porous material.
 14. The boiling heattransfer device according to claim 1, wherein a nozzle for pouring inrefrigerant is provided at an upper side corner portion of the heatdissipating portion.